MyBatis Plus

国产的开源框架，基于 MyBatis

核心功能就是简化 MyBatis 的开发，提高效率。

MyBatis Plus 快速上手

Spring Boot(2.3.0) + MyBatis Plus（国产的开源框架，并没有接入到 Spring 官方孵化器中）

1、创建 Maven 工程

2、pom.xml 引入 MyBatis Plus 的依赖

<dependency>
    <groupId>com.baomidou</groupId>
    <artifactId>mybatis-plus-boot-starter</artifactId>
    <version>3.3.1.tmp</version>
</dependency>

3、创建实体类

package com.southwind.mybatisplus.entity;

import lombok.Data;

@Data
public class User {
    private Integer id;
    private String name;
    private Integer age;
}

4、创建 Mapper 接口

package com.southwind.mybatisplus.mapper;

import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import com.southwind.mybatisplus.entity.User;

public interface UserMapper extends BaseMapper<User> {

}

5、application.yml

spring:
  datasource:
    driver-class-name: com.mysql.cj.jdbc.Driver
    url: jdbc:mysql://localhost:3306/db?useUnicode=true&characterEncoding=UTF-8
    username: root
    password: root
    
    //这样可以打印出来看sql语句
mybatis-plus:
  configuration:
    log-impl: org.apache.ibatis.logging.stdout.StdOutImpl

6、启动类需要添加 @MapperScan("mapper所在的包")，否则无法加载 Mppaer bean。

package com.southwind.mybatisplus;

import org.mybatis.spring.annotation.MapperScan;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
@MapperScan("com.southwind.mybatisplus.mapper")
public class MybatisplusApplication {

    public static void main(String[] args) {
        SpringApplication.run(MybatisplusApplication.class, args);
    }

}

7、测试

package com.southwind.mybatisplus.mapper;

import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;

@SpringBootTest
class UserMapperTest {

    @Autowired
    private UserMapper mapper;

    @Test
    void test(){
        mapper.selectList(null).forEach(System.out::println);
    }

}

默认对应类名=表名，使用注解之后就不同

常用注解

@TableName

映射数据库的表名

package com.southwind.mybatisplus.entity;

import com.baomidou.mybatisplus.annotation.TableName;
import lombok.Data;

@Data
@TableName(value = "user")
public class Account {
    private Integer id;
    private String name;
    private Integer age;
}

@TableId

设置主键映射，value 映射主键字段名

type 设置主键类型，主键的生成策略，

AUTO(0),
NONE(1),
INPUT(2),
ASSIGN_ID(3),
ASSIGN_UUID(4),
/** @deprecated */
@Deprecated
ID_WORKER(3),
/** @deprecated */
@Deprecated
ID_WORKER_STR(3),
/** @deprecated */
@Deprecated
UUID(4);

值	描述
AUTO	数据库自增
NONE	MP set 主键，雪花算法实现
INPUT	需要开发者手动赋值
ASSIGN_ID	MP 分配 ID，Long、Integer、String
ASSIGN_UUID	分配 UUID，Strinig

INPUT 如果开发者没有手动赋值，则数据库通过自增的方式给主键赋值，如果开发者手动赋值，则存入该值。

AUTO 默认就是数据库自增，开发者无需赋值。

ASSIGN_ID MP 自动赋值，雪花算法。

ASSIGN_UUID 主键的数据类型必须是 String，自动生成 UUID 进行赋值

@TableField

映射非主键字段，value 映射字段名

exist 表示是否为数据库字段 false，如果实体类中的成员变量在数据库中没有对应的字段，则可以使用 exist，VO、DTO，前端需要什么就设置什么，方便你我他

select 表示是否查询该字段

fill 表示是否自动填充，将对象存入数据库的时候，由 MyBatis Plus 自动给某些字段赋值，create_time、update_time

1、给表添加 create_time、update_time 字段

2、实体类中添加成员变量

package com.southwind.mybatisplus.entity;

import com.baomidou.mybatisplus.annotation.FieldFill;
import com.baomidou.mybatisplus.annotation.TableField;
import com.baomidou.mybatisplus.annotation.TableId;
import com.baomidou.mybatisplus.annotation.TableName;
import lombok.Data;

import java.util.Date;

@Data
@TableName(value = "user")
public class User {
    @TableId
    private String id;
    @TableField(value = "name",select = false)
    private String title;
    private Integer age;
    @TableField(exist = false)
    private String gender;
    @TableField(fill = FieldFill.INSERT)
    private Date createTime;
    @TableField(fill = FieldFill.INSERT_UPDATE)
    private Date updateTime;
}

3、创建自动填充处理器

package com.southwind.mybatisplus.handler;

import com.baomidou.mybatisplus.core.handlers.MetaObjectHandler;
import org.apache.ibatis.reflection.MetaObject;
import org.springframework.stereotype.Component;

import java.util.Date;

@Component
public class MyMetaObjectHandler implements MetaObjectHandler {
    @Override
    public void insertFill(MetaObject metaObject) {
        this.setFieldValByName("createTime",new Date(),metaObject);
        this.setFieldValByName("updateTime",new Date(),metaObject);
    }

    @Override
    public void updateFill(MetaObject metaObject) {
        this.setFieldValByName("updateTime",new Date(),metaObject);
    }
}

@Version

标记乐观锁，通过 version 字段来保证数据的安全性，当修改数据的时候，会以 version 作为条件，当条件成立的时候才会修改成功。

version = 2

线程 1:update ... set version = 2 where version = 1

线程2 ：update ... set version = 2 where version = 1

1、数据库表添加 version 字段，默认值为 1

2、实体类添加 version 成员变量，并且添加 @Version

package com.southwind.mybatisplus.entity;

import com.baomidou.mybatisplus.annotation.*;
import lombok.Data;

import java.util.Date;

@Data
@TableName(value = "user")
public class User {
    @TableId
    private String id;
    @TableField(value = "name",select = false)
    private String title;
    private Integer age;
    @TableField(exist = false)
    private String gender;
    @TableField(fill = FieldFill.INSERT)
    private Date createTime;
    @TableField(fill = FieldFill.INSERT_UPDATE)
    private Date updateTime;
    @Version
    private Integer version;
}

3、注册配置类

package com.southwind.mybatisplus.config;

import com.baomidou.mybatisplus.extension.plugins.OptimisticLockerInterceptor;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class MyBatisPlusConfig {
    
    @Bean
    public OptimisticLockerInterceptor optimisticLockerInterceptor(){
        return new OptimisticLockerInterceptor();
    }
    
}

@EnumValue

1、通用枚举类注解，将数据库字段映射成实体类的枚举类型成员变量

package com.southwind.mybatisplus.enums;

import com.baomidou.mybatisplus.annotation.EnumValue;

public enum StatusEnum {
    WORK(1,"上班"),
    REST(0,"休息");

    StatusEnum(Integer code, String msg) {
        this.code = code;
        this.msg = msg;
    }

    @EnumValue
    private Integer code;
    private String msg;
}

package com.southwind.mybatisplus.entity;

import com.baomidou.mybatisplus.annotation.*;
import com.southwind.mybatisplus.enums.StatusEnum;
import lombok.Data;

import java.util.Date;

@Data
@TableName(value = "user")
public class User {
    @TableId
    private String id;
    @TableField(value = "name",select = false)
    private String title;
    private Integer age;
    @TableField(exist = false)
    private String gender;
    @TableField(fill = FieldFill.INSERT)
    private Date createTime;
    @TableField(fill = FieldFill.INSERT_UPDATE)
    private Date updateTime;
    @Version
    private Integer version;
    private StatusEnum status;
}

application.yml

type-enums-package: 
  com.southwind.mybatisplus.enums

2、实现接口

package com.southwind.mybatisplus.enums;

import com.baomidou.mybatisplus.core.enums.IEnum;

public enum AgeEnum implements IEnum<Integer> {
    ONE(1,"一岁"),
    TWO(2,"两岁"),
    THREE(3,"三岁");

    private Integer code;
    private String msg;

    AgeEnum(Integer code, String msg) {
        this.code = code;
        this.msg = msg;
    }

    @Override
    public Integer getValue() {
        return this.code;
    }
}

@TableLogic

映射逻辑删除

1、数据表添加 deleted 字段

2、实体类添加注解

package com.southwind.mybatisplus.entity;

import com.baomidou.mybatisplus.annotation.*;
import com.southwind.mybatisplus.enums.AgeEnum;
import com.southwind.mybatisplus.enums.StatusEnum;
import lombok.Data;

import java.util.Date;

@Data
@TableName(value = "user")
public class User {
    @TableId
    private String id;
    @TableField(value = "name",select = false)
    private String title;
    private AgeEnum age;
    @TableField(exist = false)
    private String gender;
    @TableField(fill = FieldFill.INSERT)
    private Date createTime;
    @TableField(fill = FieldFill.INSERT_UPDATE)
    private Date updateTime;
    @Version
    private Integer version;
    @TableField(value = "status")
    private StatusEnum statusEnum;
    @TableLogic
    private Integer deleted;
}

3、application.yml 添加配置

global-config:
  db-config:
    logic-not-delete-value: 0
    logic-delete-value: 1

查询

//mapper.selectList(null);
QueryWrapper wrapper = new QueryWrapper();
//        Map<String,Object> map = new HashMap<>();
//        map.put("name","小红");
//        map.put("age",3);
//        wrapper.allEq(map);
//        wrapper.gt("age",2);
//        wrapper.ne("name","小红");
//        wrapper.ge("age",2);
这个可以做不等值查询


//like '%小'
//        wrapper.likeLeft("name","小");
//like '小%'
//        wrapper.likeRight("name","小");

//inSQL
//        wrapper.inSql("id","select id from user where id < 10");
//        wrapper.inSql("age","select age from user where age > 3");
联合查询
    等同于from user where (id in (select id from user where id < 10)  and age in (select age from user where age > 3))类似

//        wrapper.orderByDesc("age");
    升序排列输出

//        wrapper.orderByAsc("age");
//        wrapper.having("id > 8");
    升序排列并且只输出id大于八的

mapper.selectList(wrapper).forEach(System.out::println);

//        System.out.println(mapper.selectById(7));
//        mapper.selectBatchIds(Arrays.asList(7,8,9)).forEach(System.out::println);
查询多个id都查出来

//Map 只能做等值判断，逻辑判断需要使用 Wrapper 来处理
//        Map<String,Object> map = new HashMap<>();
//        map.put("id",7);
//        mapper.selectByMap(map).forEach(System.out::println);

QueryWrapper wrapper = new QueryWrapper();
wrapper.eq("id",7);
////        System.out.println(mapper.selectCount(wrapper));
返回记录数量

    //
    
    将查询的结果集封装到Map中
//        mapper.selectMaps(wrapper).forEach(System.out::println);
//        System.out.println("-------------------");
//        mapper.selectList(wrapper).forEach(System.out::println);

//分页查询
//        Page<User> page = new Page<>(2,2);
//        Page<User> result = mapper.selectPage(page,null);
//        System.out.println(result.getSize());
//        System.out.println(result.getTotal());
//        result.getRecords().forEach(System.out::println);

   封装结果到map集合里
//        Page<Map<String,Object>> page = new Page<>(1,2);
//        mapper.selectMapsPage(page,null).getRecords().forEach(System.out::println);

    拿出所有主键
//        mapper.selectObjs(null).forEach(System.out::println);

查询一条数据
System.out.println(mapper.selectOne(wrapper));

自定义 SQL（多表关联查询）

package com.southwind.mybatisplus.entity;

import lombok.Data;

@Data
public class ProductVO {
    private Integer category;
    private Integer count;
    private String description;
    private Integer userId;
    private String userName;
}

package com.southwind.mybatisplus.mapper;

import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import com.southwind.mybatisplus.entity.ProductVO;
import com.southwind.mybatisplus.entity.User;
import org.apache.ibatis.annotations.Select;

import java.util.List;

public interface UserMapper extends BaseMapper<User> {
    起了一个别名，避免少了
    @Select("select p.*,u.name userName from product p,user u where p.user_id = u.id and u.id = #{id}")
    List<ProductVO> productList(Integer id);
}

添加

User user = new User();
user.setTitle("小明");
user.setAge(22);
mapper.insert(user);
System.out.println(user);

删除

//mapper.deleteById(1);
//        mapper.deleteBatchIds(Arrays.asList(7,8));
//        QueryWrapper wrapper = new QueryWrapper();
//        wrapper.eq("age",14);
//        mapper.delete(wrapper);

Map<String,Object> map = new HashMap<>();
map.put("id",10);
mapper.deleteByMap(map);

修改

//        //update ... version = 3 where version = 2
//        User user = mapper.selectById(7);
//        user.setTitle("一号");
//
//        //update ... version = 3 where version = 2
//        User user1 = mapper.selectById(7);
//        user1.setTitle("二号");
//
//        mapper.updateById(user1);
//        mapper.updateById(user);

User user = mapper.selectById(1);
user.setTitle("小红");
QueryWrapper wrapper = new QueryWrapper();
wrapper.eq("age",22);
mapper.update(user,wrapper);

返给视图的我们建的实体类就命名VO，从数据库到对象的就叫DTO

MyBatisPlus 自动生成

根据数据表自动生成实体类、Mapper、Service、ServiceImpl、Controller

1、pom.xml 导入 MyBatis Plus Generator

<dependency>
    <groupId>com.baomidou</groupId>
    <artifactId>mybatis-plus-generator</artifactId>
    <version>3.3.1.tmp</version>
</dependency>

<dependency>
    <groupId>org.apache.velocity</groupId>
    <artifactId>velocity</artifactId>
    <version>1.7</version>
</dependency>

Velocity（默认）、Freemarker、Beetl

2、启动类

package com.southwind.mybatisplus;

import com.baomidou.mybatisplus.annotation.DbType;
import com.baomidou.mybatisplus.generator.AutoGenerator;
import com.baomidou.mybatisplus.generator.config.DataSourceConfig;
import com.baomidou.mybatisplus.generator.config.GlobalConfig;
import com.baomidou.mybatisplus.generator.config.PackageConfig;
import com.baomidou.mybatisplus.generator.config.StrategyConfig;
import com.baomidou.mybatisplus.generator.config.rules.NamingStrategy;

public class Main {
    public static void main(String[] args) {
        //创建generator对象
        AutoGenerator autoGenerator = new AutoGenerator();
        //数据源
        DataSourceConfig dataSourceConfig = new DataSourceConfig();
        dataSourceConfig.setDbType(DbType.MYSQL);
        dataSourceConfig.setUrl("jdbc:mysql://ip:3306/db?useUnicode=true&characterEncoding=UTF-8");
        dataSourceConfig.setUsername("root");
        dataSourceConfig.setPassword("root");
        dataSourceConfig.setDriverName("com.mysql.cj.jdbc.Driver");
        autoGenerator.setDataSource(dataSourceConfig);
        //全局配置
        GlobalConfig globalConfig = new GlobalConfig();
        globalConfig.setOutputDir(System.getProperty("user.dir")+"/src/main/java");
        //上面都是可套用
        globalConfig.setOpen(false);
        //创建作者
        globalConfig.setAuthor("southwind");
        globalConfig.setServiceName("%sService");
        autoGenerator.setGlobalConfig(globalConfig);
        //包信息
        PackageConfig packageConfig = new PackageConfig();
        //这里要改
        packageConfig.setParent("com.southwind.mybatisplus");
        packageConfig.setModuleName("generator");
        packageConfig.setController("controller");
        packageConfig.setService("service");
        packageConfig.setServiceImpl("service.impl");
        packageConfig.setMapper("mapper");
        packageConfig.setEntity("entity");
        autoGenerator.setPackageInfo(packageConfig);
        //配置策略
        StrategyConfig strategyConfig = new StrategyConfig();
        strategyConfig.setEntityLombokModel(true);
        strategyConfig.setNaming(NamingStrategy.underline_to_camel);
        strategyConfig.setColumnNaming(NamingStrategy.underline_to_camel);
        autoGenerator.setStrategy(strategyConfig);

        autoGenerator.execute();
    }
}

参考文章

4小时学会MyBatis Plus通俗易懂，从入门到部署上线

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